Antenna and portable wireless device

ABSTRACT

A planar inverted-F antenna has a ground plate provided on a circuit board, a planar radiator, a short line, a feed line, and an inductance element. The radiator is disposed facing the ground plate. The short line and the feed line are connected to the radiator. The inductance element is connected electrically between the ground plate and the short line.

This application is a U.S. national phase application of PCTinternational application PCT/JP2004/014574.

TECHNICAL FIELD

The present invention relates to a planar inverted-F antenna and amobile communication device using the same such as a portable telephoneor a personal handyphone.

BACKGROUND ART

Terminals for mobile communication devices such as portable telephonesor the like are progressing in downsizing. Most mobile communicationdevices are equipped with a built-in antenna inside housing recently.FIG. 7A shows a perspective view of a conventional mobile communicationdevice, and FIG. 7B shows a perspective side view of the same.

Circuit board 101 is disposed in housing 100. Display 109, input unit111, circuit 110 and planar inverted-F antenna (hereafter referred to“antenna”) 108 are disposed in housing 100, and are connected to circuitboard 101 respectively.

FIG. 8 shows an exploded perspective view of conventional antenna 108.Ground plate 102 is provided on circuit board 101. Radiator 103 isdisposed facing circuit board 101. Short line 104 connects radiator 103with ground plate 102. Feed line 105 is connected to radiator 103. Feedterminal 106 connects feed line 105 with a circuit (not shown). Slit 107is formed in radiator 103.

By adjusting a gap distance between short line 104 and feed line 105,the impedance of antenna 108 is varied to implement an impedancematching. A length of slit 107 is varied to adjust the gap distancebetween short line 104 and feed line 105. Japanese Patent ApplicationUnexamined Publication No. H4-157908 discloses an example of suchantenna.

To implement the impedance matching by adjusting the length of slit 107,however, slit 107 must be extended causing radiator 103 to have a largerarea. This would result in a larger shape of antenna 108, and eventuallycause a difficulty in the device downsizing. Moreover, extending slit107 requires changing the geometry of antenna 108 itself that needsredesigning of molds to produce antenna 108, thus it is not an easytask.

SUMMARY OF THE INVENTION

A planar inverted-F antenna of the present invention has a ground plateprovided on a circuit board, a planar radiator, a short line, a feedline, and an inductance element. The radiator is disposed facing theground plate. The short line and the feed line are connected to theradiator. The inductance element connects the ground plate with theshort line electrically. By connecting the inductance element to adjustthe antenna impedance, a downsized antenna capable of adjusting theimpedance without changing the antenna form can be achieved. The mobilecommunication device disclosed of the present invention has a housing, acircuit board, an aforementioned antenna provided in the housing, theantenna connected to the circuit board, a circuit, an output unit and aninput unit, the circuit, the output unit and the input unit connected tothe circuit board respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a perspective view of a mobile communication deviceaccording to an exemplary embodiment of the present invention.

FIG. 1B shows a perspective side view of the mobile communication deviceshown in FIG. 1A.

FIG. 2 shows an exploded perspective view of a planar inverted-F antennaaccording to the exemplary embodiment of the present invention.

FIG. 3 shows an impedance characteristic of a conventional planarinverted-F antenna.

FIG. 4 shows an impedance characteristic of the planar inverted-Fantenna according to the exemplary embodiment of the present invention.

FIG. 5 shows an exploded perspective view of another planar inverted-Fantenna according to the exemplary embodiment of the present invention.

FIG. 6 shows an exploded perspective view of still another planarinverted-F antenna used according to the exemplary embodiment of thepresent invention.

FIG. 7A shows a perspective view of a conventional mobile communicationdevice.

FIG. 7B shows a perspective side view of the conventional mobilecommunication device.

FIG. 8 shows an exploded perspective view of the conventional planarinverted-F antenna.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1A shows a perspective view of the mobile communication deviceaccording to the exemplary embodiment of the present invention, and FIG.1B a perspective side view. Circuit board 11 is disposed in housing 1.Output unit 3, input unit 4, circuit 5 and planar inverted-F antenna(antenna) 6A are connected to circuit board 11 respectively in housing1. Circuit 5 has a capability of at least sending/receivingcommunication from external through antenna 6A, showing externalinformation or input data from input unit 4 on output unit 3. That is,output unit 3 shows information input into circuit 5. Input unit 4receives information input and sends it to circuit 5. A rotary encoderor a mike can replace input unit 4 shown as a ten-key in FIG. 1A.Similarly, a speaker can replace output unit 3 that is shown as adisplaying device such as LCD panel or the like.

FIG. 2 shows an exploded perspective view of antenna 6A according to theexemplary embodiment of the present invention. Ground plate 12 isprovided on circuit board 11, and planar radiator 13 is disposed overcircuit board 11 facing ground plate 12. Short line 14 and feed line 15are connected to radiator 13. Feed terminal 16 is formed on circuitboard 11 to connect feed line 15 with a circuit (not shown) on circuitboard 11. Terminal 17 formed on circuit board 11 is connected to shortline 14. As terminals 16 and 17 are provided on circuit board 11,radiator 13 can be set easily.

Chip coil 18 as an inductance element is mounted on circuit board 11 toconnect terminal 17 with ground plate 12 electrically. That is, chipcoil 18 is connected between short line 14 and ground plate 12electrically through terminal 17. Antenna 6A has radiator 13, groundplate 12, feed line 15 and short line 14. Radiator 13, ground plate 12,feed line 15 and short line 14 are made of for instance a conductivematerial such as oxygen free high conductivity copper or a resilientphosphor bronze respectively. In addition, a plastic holder or the likecan be provided between radiator 13 and ground plate 12.

The impedance of antenna 6A is the sum of the reactance of feed line 15,the reactance of short line 14, and the impedance of radiator 13connected in parallel. Distance A between feed line 15 and short line 14has to be adjusted for the impedance matching. However, achieving theimpedance matching only by adjusting distance A between feed line 15 andshort line 14 tends to be difficult along with the downsizing of antenna6A. This becomes a significant hamper in designing of a mobilecommunication device using antenna 6A. In the present exemplaryembodiment, chip coil 18 is mounted on circuit board 11 where terminal17 and ground plate 12 are connected. The configuration enables theimpedance to match easily while downsizing of the antenna is maintained.

FIG. 3 shows an impedance characteristic of antenna 108 shown in FIG. 8having no chip coil, that is a Smith-chart with distance A between feedline 15 and short line 14 of 1 mm. The chart implies that the impedancematching is achieved better when the characteristic curve locates asnear to the center (50 Ω impedance) as possible. In reality, however,characteristic curve 120 locates far from the center, causing a poorimpedance matching to the 50 Ω impedance.

The results are obtained because the distance between feed line 105 andshort line 104 is too narrow and therefore the distance must be widened.However, widening the distance or adding slits for the requiredcharacteristic would eventually cause a difficulty in downsizing orchanging of geometry of the antenna.

FIG. 4 shows an impedance characteristic of antenna 6A according to theexemplary embodiment. FIG. 4 is a Smith chart for antenna 6A withdistance A between feed line 15 and short line 14 of 1 mm, and with chipcoil 18 of 6.8 nH disposed between terminal 17 and ground plate 12. Theimpedance at a required frequency band locates approximately in thecenter of the chart as shown in the characteristic curve 30 of FIG. 4.This shows that the impedance matching can be achieved by only addingthe most suitable chip coil 18 without any change in antennaconfiguration.

As described above, varying the element value of chip coil 18 hasequivalent effects of changing the distance between feed line 15 andshort line 14, enabling antenna 6A to achieve a proper impedancematching.

Next, the configuration of another planar inverted-F antenna accordingto the exemplary embodiment is described with reference to FIG. 5. FIG.5 shows an exploded perspective view of another planar inverted-Fantenna.

The difference between antenna 6B shown in FIG. 5 and antenna 6A shownin FIG. 2 is that an inductance element is formed in circuit pattern 19provided on circuit board 11. The other configurations are identical toantenna 6A.

The configuration can form the inductance using circuit pattern 19 only,enabling antenna 6B with a cheaper production cost.

Instead of circuit pattern 19, adopting other configuration such asbonding a winding of copper wire or copper foil can provide similareffects.

Next, the configuration of still another planar inverted-F antennaaccording to the exemplary embodiment is described with reference toFIG. 6. FIG. 6 shows an exploded perspective view of still anotherplanar inverted-F antenna.

While antenna 6A has a single radiator 13 as shown in FIG. 2, antenna 6Cshown in FIG. 6 has first radiator 20 and second radiator 21. The otherconfigurations are identical to antenna 6A.

The configuration can provide antenna 6C with a capability to respond toa plurality of frequencies because first radiator 20 and second radiator21 respond respective frequencies. The mobile communication device usingsuch antenna 6C can respond to a plurality of frequencies.

INDUSTRIAL APPLICABILITY

The disclosed is a downsized antenna capable of adjusting the impedancewithout changing the antenna geometry. Such an antenna is useful formobile communication devices.

1. An antenna comprising: a circuit board; a ground plate located on thecircuit board; a planar first radiator facing the ground plate; a shortline connected to the first radiator; a feed line connected to the firstradiator; and an inductance element comprising a circuit pattern on thecircuit board, and connected electrically between the ground plate andthe short line.
 2. The antenna according to claim 1, wherein theinductance element is a chip coil.
 3. The antenna of claim 1, furthercomprising a second radiator similar to the first radiator.
 4. A mobilecommunication device comprising: a housing; an antenna of claim 1, thecircuit board located in the housing; an input unit connected to thecircuit board to receive information; and an output unit connected tothe circuit board to output information input into the circuit.
 5. Themobile communication device according to claim 4, further comprising: aterminal on the circuit board to connect the short line with theinductance element; and a feed terminal on the circuit board to connectthe circuit with the feed line.
 6. The mobile communication deviceaccording to claim 4, wherein the ground plate and the planar firstradiator of the antenna have common edges on three sides.
 7. The antennaaccording to claim 1, wherein the ground plate and the planar firstradiator have common edges on three sides.